1. Field of the Invention
The invention relates to medical devices and, more particularly, to methods and devices for forming a percutaneous channel.
2. Description of the Related Art
A wide variety of diagnostic or therapeutic procedures involves the introduction of a device through a natural or artificially created access pathway. A general objective of access systems, which have been developed for this purpose, is to minimize the cross-sectional area of the puncture, while maximizing the available space for the diagnostic or therapeutic instrument. These procedures include, among others, a wide variety of laparoscopic diagnostic and therapeutic interventional procedures.
Percutaneous nephrostomy is an example of one type of therapeutic interventional procedure that requires an artificially created pathway. Percutaneous nephrostomy is a minimally invasive procedure that can be used to provide percutaneous access to the upper urinary tract. At first, percutaneous nephrostomy was used only for urinary diversion but now it can be used for more complex procedures such as stone extraction, integrate endopyelotomy, and resection of transitional cell carcinoma of the upper urinary tract.
In many percutaneous nephrostomy systems, a stiff guidewire is first placed into the renal collection system through the renal parenchyma and the ureter under fluoroscopic control. A second “safety wire” may be placed with a dual lumen catheter for maintaining the tract should the first wire become dislodged or kinked.
Once guidewire control is established, a dilator sheath is used to create the tract and establish a rigid working lumen. One technique involves advancing a flexible, 8 French, tapered catheter over the first guidewire to provide guidewire protection as well as a stable path for the placement of larger diameter dilators and sheaths. The larger diameter sheaths are sequentially advanced over the catheter and each other until an approximately 34 French (11 to 12 mm diameter) tract is established. The inner sheaths or dilators may then be sequentially removed such that the outermost sheath defines a working lumen. In this system, tract formation is accomplished by the angular shearing force of each subsequent sheath placement, which cuts a path through the tissue. Because axial pressure is required to advance and place each sheath, care must be taken to avoid kinking the tapered catheter and/or advancing the sheaths too far and potentially perforating the renal pelvis. This technique requires a large number of steps, requires a large amount of force that can be readily misdirected, and is relatively time consuming.
A more recent technique utilizes a balloon that is advanced over the first guide wire. Once in place in the renal pelvis, the balloon is inflated with a dilute contrast media solution to enlarge the tract. Once the balloon is inflated to a suitable diameter, a rigid sheath is advanced over the balloon. Advancing the rigid sheath over the balloon typically requires applying axial force to the sheath as well as rotation of the sheath relative to the balloon. The balloon can then be deflated and removed from the rigid sheath so that the rigid sheath may define a working lumen. In general, this technique is considered less traumatic than the previously described technique of nested, concentric dilators. Nevertheless, placement of the rigid sheath still involves angular shearing forces and several steps. Expandable percutaneous sheaths have also been introduced to the market and these sheaths have the advantage of introduction at a small diameter and then being expanded to larger diameters for use. The use of a surrounding jacket has become standard when inserting expandable percutaneous access sheaths. The jacket surrounds and restrains the expandable portion of the sheath, and maintains the small diameter prior to and during insertion into the body. The presence of the jacket, which needs to be split or otherwise released, reduces the net expansion force of the sheath and compromises its function.
Additional information regarding percutaneous nephrostomy can be found in McDougall, E. Mo, et al. (2002), Percutaneous Approaches to the Upper Urinary Tract, Campbell's Urology, 8th ed, vol. 4, pp. 3320-3357, Chapter 98, Philadelphia, Saunders.